MailSpring is an open source email client application which support Windows, MacOSX and Linux. Mailspring supports all IMAP providers, including Gmail, Office 365 and iCloud. It sports features such as an unified inbox, snoozing, reminders, templates, offline search, and support for Gmail labels. Mailspring is free for Mac, Windows, and Linux. However, if you use features like Snooze, Send Later, Send Reminders and Read Receipts often, you'll need to purchase a subscription to Mailspring Pro within the app. Mailspring Pro costs $8/mo and helps support the development of Mailspring.

About Mailspring ID

When you install Mailspring for the first time, you'll need to create a Mailspring ID. Your Mailspring ID is separate from your email account(s) and you can use any email address or password you'd like. Mailspring does not store your email passwords in the cloud. It syncs only the minimal amount of data required to power features like snooze, send later, etc., and uses a hashing mechanism to identify emails and associate it's metadata across installs.

If you create a Mailspring ID and later decide you don't want one, you can sign in to the Mailspring ID dashboard (https://id.getmailspring.com) at any time and permanently delete your account and all data associated with it.

Mailspring 1.4.2 fixes:

Mailspring no longer attempts CRAM-MD5 SMTP auth instead of PLAIN or LOGIN when both are supported.

CRAM-MD5 and DIGEST-MD5 require you've exchanged a shared secret with the SMTP server which is almost never the case.

Mark as Spam now appears in the right-click dropdown menu for threads.

The IMAP/SMTP port dropdowns no longer "stick" the first time you change them during setup.

Mailspring now lets you know if your SMTP server refused to relay a test message during setup.

Mailspring now correctly supports SMTP accounts that do not require a username or password.

Open and link tracking now work correctly for accounts using Courier IMAP (where sent messages do not appear until re-selecting the folder via IMAP.)